Amplitude equalizer of speech sound waves



Oct. 25, 1960 AMPLITUDE Eil M. v. KALFAIAN EQUALIZER oF SPEECH SOUNDWAVES i Filed Jan. 19, 1960 United. States Patent lice,

AMPLITUDE EQUALIZER F SPEECH SOUND WAVES Meguer V. Kalfaian, 962Hyperion Ave., Los Angeles, Calif.

Filed Jan. 19, 1960, Ser. No. 3,347

1 Claim. (Cl. 330144) This invention relates to Iautomatic amplitudecontrol systems, and particularly to a system for normalizing theamplitude of propagated speech sound waves to -a constamt-peak amplitudelevel. Its main object is to compress and expand the amplitude ofpropagated speech sound waves stepwise at the fundamental frequencies ofsaid sound waves, so that constant peak-amplitude may be obtainedregardless vof the speed of phonation. A further object is to provideamplitude equalization Without resorting to loss of voice quality orintelligibility.

In various forms of speech sound wave production and reproduction, it isoften desired that the wide variations ofV amplitude in speech soundwaves, as originated in the vocal system, are synthetically compressedto a standard peak amplitude. Automatic volume control systems are usedconventionally, for example, in radio circuitry. These systems, however,are useful only for slow amplitude variations, and if they are `arrangedto control fast amplitude variations of the speech sound waves, thevoice quality is completely lost; although substantial amount ofintelligibility may be preserved. VAccordingly, the system disclosedherein is contemplated .to provide complete equalization of the speechsound wave peaks, with negligible loss of voice quality, but without anyloss of intelligibility. Such amplitude equalization without loss ofvoice quality may be obtained by shifting the amplitudes of sound wavepatterns stepwise without distorting their waveforms; the condition ofwhich I have shown to be true by actual tests. Briefly in accordancewith the invention, the original speech sound waves are applied to again controllable amplifier. A gain-reducing feedback isV first passedthrough a peak reference bias source, .and stored in a capacitor, so asto reduce the gain of the amplifier in constant state. The fundamentalfrequencies of the speech sound waves (wave patterns) are selected, andnarrow pulse signals are produced at the peaks of said Wave patterns.These pulse signals are then utilized to modify the storage across saidcapacitor, so 'as to change the gain of said amplifier stepwiseaccording to the amplitude of each of the incoming Wave pattern of thespeech 4sound wave. rllhe nature of such .a system will be app-arentfrom the following specification, and in conjunction with theaccompanying schematic arrangement of the figure.- v

Referring to the arrangement of the figure, the speech sound wave isapplied to-one of the `control grids, for

2,958,047 Patented Oct. 25, 1.967() obtained from battery B2. From thetwo end terminals of inductor L1, there are connected diodes D1 and D2to the control grids G1 of tubes V1 and V2, respectively. These diodesare so polarized that only negative signals developed across inductor L1are admitted therethrough.' T-he positive bias of battery B2, therefore,prevents ad-V mittance through diodes Dl'and D2. until the negativesignal across L1 exceeds the potential of B2, for charging eithercapacitor C1 or C2 in negative polarities. There are used two vacuumtubes, V3 and V4, in oppositely polarized parallel connections with thediodes D3 and D2, respectively. The oppositely polarized vacuum tubes V3and V4 are used to charge the capacitors C1 and C2 positively duringAgain shifting pulse periods, and are normally rendered inoperative byhigh negative biases impressed upon their control grids. 'Ilhesenegative biases are produced across resistors R5 and R6 by way of normalanode current 'draw through normally conducting tubes V5 and V6. Inorder to develop negative potentials across resistors R5 and R6, theanode elements of tubes V5 and V6 are arranged to receive near groundpotential, and their cathodes to receive negative potential from batteryB3, while the anode elements of tubes V1 and V2 receive positivepotential from battery B4. The control grids of tubes V5 and V6 areconnected to their cathodes through a common load resistor R7, so thatthese tubes are norm-ally in conductive states.

In operation, the voice sound signals are generated across inputresistors R1 and R27 and applied to the control grids G2 of gaincontrollable amplifier tubes V1 and V2. Due to the push-pull arrangementof these tubes, the amplified sound waves across anode circuit resistorsR3 and R4 -appear linearly. These amplified waves are coupled to theinductive load L1, the signals across which are fed back in push-pull tothe control grids G1 of tubes V1 and V2, in series with diodes D1 andD2. Because of the positive bias of battery B2, the negatively developedsignals across inductor L1 pass thro-ugh the diodes D1 yand D2 only whenthey rise above this bias level, and charge either cap-acitor C1 or C2negatively. The negative charge across either one of these capacitorsreduces the gain of its associate amplifier tube until the signal acrossinductor L1 equals the bias potential of battery B2, whereupon furthercharging of the capacitors stops. In normal speech sound Waves thepositive and negative peaks are not symmetric, and accordingly, thepush-pull arrangement of amplifier tubes V1 and V2 facilitates amplitudeequalization of both polar-ities. Thus when a high peak of the inputvoice signal arrives, the amplifier gain is reduced to a referencemagnitude, and remains in such a state thereon, so that example, G2, ofdual control vacuum tubes V1 and V2, from across resistors R1 and R2,which are connected iig/.lay of =capacitors C1 and C2, respectively. Theamplified waves across R3 and R4 are coupled capaci-tively (by C3 andC4) in push-pull to an inductive load L1, the center tap of which isconnected to the cathodes of tubes V1 and V2 in series with a positivepotential, as

the amplifier functions linearly. The peak amplitude of -a followingwave pattern of the speech sound wave may have a lower amplitude thanthe preceding one, and accordingly, the gain of the amplifier must bereadjusted at the arrival of the following peak.

As described in my.U.S. Patent No. 2,872,517, February 3, 1959, thefundamental frequencies of speech sound waves are represented by thepresence of trains ofl wave patterns, each terminating a high peakedwave. Thus by selecting these high peaked waves, the fundamentalfrequencies of speech sound waves may be represented, as described bywayV of a schematic arrangement in saidpatent. Accordingly, the block-1in the ligure represents a fundamental, frequency selector, which isarranged to produce negative pulses at said high peaked waveshasindicated by the pulse waves 2 above block 1. These negative pulses aresimultaneously applied upon the'control grids of tubes VS and V6(through coupling capacitor C13), which momentarily becomenon-conductive, and remove the negative bias voltages across resistorsR5 `and R6. The tubes V3 and V4 in turn become con- 3 v ductive, andbecause of their oppositely polarized connections in parallel withdiodes D1 and D2, the capacitors C1 and C2 discharge during the shortpulse period. This discharge may be more than necessary, but the diodesD1 and D2 will immediately readjust their charges to the requirednegative potentials. During such voltage adjustment, a high amplitudepulse may appear across the output resistors R3 and R4, but a smallcapacitor connected in parallel with the inductor L1 is found tosuppress satisfactorily any pulse generated in L1 without interferingwith the voice signals.

With the above given explanation, it is seen that the arrangement of thegure is capable of equalizing the varying amplitudes of speech soundwaves stepwise, as proceeds wave pattern after wave pattern, withoutdistorting their waveshapes. Such distortionless amplitude equalizationwill, accordingly, providehigh quality and high intelligibility of thevoice sounds, as I have shown by actual tests. Ideal conditions,however, are often difficult to attain, because of imperfect componentparts that may be utilized. For example, the amplifier tubes V1 and V2must provide high ratio of gain control with high linearity, thecondition of which is very difficult to obtain, even though push-pulldrive is utilized. Accordingly, two identical gain controlling stageswill provide the requred gain control, with moderate drive to eachstage, thereof. As the second stage is identical to the first stage,further description of same is not necessary. But for referencepurposes, the component parts may be identified, as in the following:

The output voice signal across inductor L1 is coupled in push-pull tothe control grids G2 of gain controllable amplifier tubes V7 and V8,through coupling capacitors C5, C6, and from across load resistors R8and R9, which are further terminated common to ground in series withbias battery B5. The amplified sound waves across output resistors R10and R11 are coupled to output load in ductor L2 through couplingcapacitors C9 and C10. The two end terminals of center tapped inductorL2 are coupled in push-pull to the control grids G1 of amplifier tubesV7 and V8, through polarized diodes D3 and D4, the anode terminals ofwhich are further connected to storage capacitors C7 and C8,respectively, terminated common to ground. The center tap of inductor L2is connected to ground in series with peak limiting positive bias ofbattery B6, so that the capacitors C7 and C8 are charged negativelythrough diodes D3 and D4 when the negative signal developed across L2exceeds the limiting potential of battery B6; the latter of which may bethe same as battery B2. The discharge of capacitors C7 and C8 isestablished by vacuum tubes V9 and V10, which are normally renderedinoperative by high negative bias potentials upon their control grids,developed across resistors R12 and R13. These negative bias potentialsare developed by normally conductive tubes V11 and V12, the anodeterminals of which are connected to the control grids of V9 and V10,respectively. Since the gain controlling storage capacitors C1, C2, andC7, C8 of both stages are discharged simultaneously during a pulseperiod, both the control grids and cathodes of V11 and V12 are connectedin parallel with the grids and cathodes of tubes V and V6. The finalamplitude equalized voice sound waves are then taken from across outputinductor L2, either directly, or through the coupling capacitors C11 andC12.

In actual practice, the inductors L1 and L2 had been substituted byresistive elements. But due to the capacitive coupling, the voltageacross said resistive elements varied erratically during dischargeperiods of the storage capacitors. Accordingly, the use of inductiveelements is suggested more desirable; although resistive elements mayalso be used, if so desired. Each type has an advantage,

for example, the use of resistive elements will deliver a wide band offrequencies with lesser cost, while the inductive element will eliminatesome noise with higher cost; especially when high quality parts areused. If desired, the resistors R3, R4, R10, R11, coupling capacitorsC3, C4, C9, C10 and inductors L1, L2 may be eliminated, and transformerssubstituted instead. This latter arrangement will provide higher qualitysignal output, but it becomes more complicated to adjust the timing ofpulse periods during which the gain suppressing storage capacitors aredischarged for the required stepwise gain adjustments of the twoseparate amplifier stages. It is, of course, obvious that transistors,for example, the types having dual base controls, may be utilized withthe arrangement of the figure.

With the above given specification of the arrangement of the figure,itis readily suggested that various substitutions, modifications andadaptations are possible, without deparating from the true spirit andscope of the invention.

What I claim is:

In complex waves having random variations in amplitude peaks, a systemof equalizing the amplitudes of said peaks, comprising means forproducing said complex waves; means for producing pulse signals at saidpeaks; first and second gain controllable amplifier means, eachcomprising an electric discharge device having an emitter, first andsecond gain controlling electrodes, and a collector electrode,respectively; means for applying said produced complex waves to the gaincontrolling first electrodes of said first and second amplifier means inoppositely poled directions for amplification of same in theirrespective collector electrodes; an inductive impedance means havingfirst and second terminals and a center tap; means for coupling saidamplified complex waves in said collector electrodes of the first andsecond amplifier means to the first and second terminals of saidimpedance means, respectively; a peak limiting bias voltage source, andmeans for connecting same from said center tap to the emitter electrodesof said first and second electric discharge devices; first and secondrectifier means and first and second storage means; means for couplingthe first rectifier means and the first storage means in series with thefirst terminal of said impedance means and the second electrode of saidfirst amplifier means in gain reducing direction, so that said storagemeans is charged in substantially a steady state for gain reduction whenthe peak of said amplified complex wave is higher than said peaklimiting bias source; means for coupling the second rectifier means andthe second storage means in series with the second terminal of saidimpedance means and the second electrode of said second amplifier meansin gain reducing direction, so that said storage means is charged insubstantially a steady state for gain reduction when the peak of saidamplified complex wave is higher than said peak limiting bias source;third and fourth electric discharge devices, each having an emitter, anadmittance control electrode and a collector; means for coupling saidthird and fourth devices oppositely polarized across said first andsecond rectifier means, resepctively, for discharging the steady statecharges of said first and second storage devices; a normal admittanceblocking bias source upon the electrodes of said third and fourthelectric discharge devices; and means for applying said pulse signals tolast said electrodes for cancelling said blocking bias, whereby tomodify said steady state storages, and thereby obtaining said stepwiseamplitude equalization across said impedance means in oppositelypolarized directions.

References Cited in the file of this patent UNITED STATES PATENTS2,883,480 Grenier Apr. 21, 1959

